This invention relates generally to a method for coating articles, and more particularly to a novel method for automatically applying powder coatings on various electronic parts, such as, for example, integrated circuits, condensers, diodes or the like.
It is conventional to have integrated circuits, condensers, diodes or the like coated several times with coating materials in the form of powder, such as, for example, powdered epoxide resins, to obtain electrically and physically perfect coatings without craters and pinholes to protect the surface of these parts and to provide high grade electrical insulation and anti-humidity characteristics.
In powder coating, articles to be coated are pre-heated prior to an application of powdered coating materials or coating surfaces are heated after the coating operation is finished. Maximum coating thickness obtainable by the powder coating at one time is approximately 200.mu. . If electronic parts are to be coated to a coating thickness of lmm by application of powdered coating materials in order to eliminate craters and pinholes from the coating surface and to impart sufficient electrical insulation and anti-humidity characteristics to the electronic parts, the powder coating operation must be repeated five times.
The heating and coating processes for powder coating are usually conducted automatically by a conveyer system for the sake of efficiency. One such conveyer system employs a conveyer which moves at constant speed, and another conveyer system employs a conveyer which moves intermittently at regular intervals during the heating and coating processes. This system is generally known as a tact system. The tact system is considered to be advantageous as compared with the system wherein the conveyer moves at constant speed, because the equipment for the coating operation is compact, the cost of equipment is lower, and the installation site is reduced. However, if multiple powder coatings are conducted by the tact system using a plane and linear type conveyer which includes one coating zone, the articles to be coated have to be replaced on the conveyer several times for the multiple coatings. To avoid this problem, coating zones must be set up at several locations along the path of the conveyer. Since the number of coatings varies depending upon the articles to be coated, it is preferable to make the conveyer round in order to achieve the multiple coatings using a conveyer line which includes one coating zone. Obviously, a vertically rotatable round conveyer is advantageous rather than a horizontally moveable round conveyer, because it can make good use of vertical spaces. The inventors have succeeded in providing a novel coating method using a vertically moveable, round tact conveyer system which is operated to synchronize the feeding and removal of the articles to be coated with the number of coatings applied thereto. According to the present invention, the articles to be coated are attached to the conveyer and removed therefrom every two tact rotations, or complete cycles, of the conveyer when the articles are to be coated two times. When the articles are to be coated three times, the articles are attached to the conveyer and removed therefrom every three tact rotations of the conveyer. Similarly, other multiple coating operations are conducted such that the number of tact rotations of the conveyer corresponds to the number of coating to be applied to the articles as desired.